This invention relates to plasma processing apparatus and methods.
Plasma processing apparatus is used in many stages of the fabrication of semiconductor devices such as in etching and deposition. As the scale size of features on these devices is reduced and the overall size of the wafers is increased, there is a need for increased plasma density and uniformity over ever-greater areas. In a related field plasma is used as a source of ion or electrons for an accelerator of these particles, which are then used for a variety of physical processes. The spatial uniformity of the extracted beam is related to the uniformity of the plasma in the source of charged particles. For the purposes of this Specification the creation of a plasma to provide a source of such particles is included in the term xe2x80x9cplasma processingxe2x80x9d.
Current practice is to attempt to determine, whether theoretically or empirically, the output which will be provided by an antenna used to generate a plasma in the chamber and then to alter the physical construction and location of the antenna and chamber so as to produce as uniform a plasma as possible. However successful these calculations are, they tend to only relate to one set of operating conditions, whilst a user would expect to be able to perform a variety of processes within a chamber which may use a variety of reactive gases.
From one aspect the invention consists in plasma processing apparatus for processing a workpiece comprising a processing chamber for receiving the workpiece at a location, a plurality of antennae for generating a plasma in the chamber, means for varying the relative outputs of the antennae, detecting means for detecting a property or parameter of the resultant plasma or process and control means for controlling the output varying means in accordance with the property or parameter detected.
For the purposes of this Specification the term xe2x80x9cantennaxe2x80x9d includes a coil or other device which is suitable for generating a plasma. It is particularly preferred that the antennae should inductively couple power to the plasma once it is initiated. The apparatus and the method of this Application are particularly suitable for use with RF driven antennae.
The detecting means includes a detector within the chamber. The detector may detect ion flux, ion energy and/or neutral particle arrival or removal rates. Indeed any property or parameter which reflects either the intensity and/or distribution of the plasma or the rate of the process being operated can be used as the basis of detection.
It is particularly preferred that the property or parameter is detected at or near the workpiece location. For example, the detector may be in the a form of Langmuir probe. It is particularly preferred that the Langmuir probe is shielded from the plasma by a semi-conductor or insulating layer, which may have a thickness in the range of a few times the Debye length of the plasma, typically 50-100 xcexcm. In general, in order to operate, the layer will have to be thin. In these arrangements the Langmuir probe is driven. For example the probe may receive intermittent RF power and the ion flux may be detected in the periods when the power is switched off by detecting the rate of discharge of a series capacitor.
The probe may be mounted in a semiconductor or insulator with a thin layer of material separating the probe from the plasma.
In the above arrangements the detector may be mounted in a semiconductor wafer so that such a wafer can be placed in a processing chamber on a support to enable a chamber to be set up for any particular process. Alternatively, and in most cases more conveniently, a detector may be located in a wafer support platen within a chamber.
Alternatively the detector may detect the properties of the plasma indirectly by monitoring the condition of the workpiece. For example, etch depth could be measured using a remote interferometer.
The detecting means may include a plurality of detectors and there may be one or more detectors associated with each antenna. The detector or detectors may detect a number of properties. The control means may control the output of each antenna in response to its associated detector or in response to the output of its detector relative to the output of at least one other detector.
The means for varying the relative outputs of the antennae may include means for varying the magnitude, frequency, or relative phase of power fed to the antennae and/or the relative position of the antennae. The objective will usually be to achieve increased homogeneity but specific inhomogeneous conditions may be maintained.
From another aspect the invention consists in a workpiece or a workpiece support including a Langmuir probe embedded therein such that the probe is covered by a layer of semiconductor or insulator.
Preferably there are a plurality of probes and the wafer or support may further include means for intermittently feeding RF power to the probes and means for monitoring the discharge of a capacitor in series with each probe whilst the RF supply is switched off.
From a still further aspect the invention consists in a method of performing a plasma process including generally the plasma in a chamber by means of a plurality of antennae, detecting or setting a property or parameter of resultant plasma or process and controlling the relative outputs of the antennae in accordance with the property or parameter detected.
Preferably there is one or more detectors associated with each antenna and the antenna is controlled on the basis of the plasma or process detected by the associated detector or detectors. Each antenna may further be controlled on the basis of the magnitude of the property or parameter detected by its associated detector relative to the corresponding magnitude for at least one other detector. More than one property or parameter may be detected.
The outputs of the antennae may be controlled by varying the magnitude frequency or relative phase of the power fed to the antenna and/or the physical position of the antennae.
The process may be performed on a workpiece and the parameter or property may be detected at or adjacent the level of the workpiece.
Although the invention has been defined above it is to be understood it includes any inventive combination of the features set out above or in the following description.